The subject matter disclosed herein relates to an impeller retention apparatus of an aircraft and, more particularly, to an impeller retention apparatus of an aircraft that includes a preload spacer.
An aircraft, such as a helicopter, includes an airframe formed to define a cabin, a main rotor and a tail rotor, which are supportively disposed at upper and tail portions of the airframe, respectively. An engine drives rotation of the main and tail rotors via a transmission system including a shaft that extends through the tail portion. In such aircraft, retention of a shaft driven impeller that is typically utilized to move air through a heat exchanger has traditionally been achieved with a threaded locknut. In many cases, the impeller would either use internal splines or a keyway as an interface with the driving shaft and be held in place with the threaded locknut.
These types of retention schemes for the impeller can give rise to a sharp corner or thread radii on the outer diameter of the shaft. These sharp corners or thread radii produce stress concentrations which ultimately can be an origin for a shaft fracture. In addition, locknuts can loosen and result in loss of preloading.